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PLANT EVOLUTION
KEY CONCEPT
Plant life began in the water and became adapted to
land.
Plant Evolution
• Evolved from green algae
(450 mya)
– Both have chlorophyll,
store energy as starch,
DNA similarities
• Green algae ancestor
– Multicellular body
– Cells w/ channels to
communicate
– Reproduce w/ sperm &
egg
• Early plants
– Low growth
• True plants evolved through natural selection.
– Ancestral charophyceans lived in areas of shallow water.
– Those that could survive longer dry periods were favored.
– First true plants probably grew at edges of water.
– True plants have embryos that develop while attached to
female parent.
Land Adaptations
stoma
• Retain Moisture
– Early plants grew near waters edge
– Cuticle: waxy coating
– Stomata: pores to allow gas exchange
Land Adaptations
• Transporting Resources
– Vascular system: tissue to transport nutrients
• Up from the roots (ex: water)
• Down from the leaves (ex: sugars)
– Allows taller growth
Land Adaptations
• Growing upright
– Large plants need to support own weight
– Lignin: hardens cell wall; gives wood strength
Land Adaptations
• Reproduction on land
– Pollen: carried by wind/animals (no water necessary)
– Seeds: hard coat protects embryo inside
Alternation of generations
• Sporophyte (diploid)
– Begins when sperm
fertilizes egg (zygote)
– Diploid zygote divides
by mitosis to create a
mature sporophyte
– Meiosis produces
haploid cells called
spores
• Gametophyte
– Haploid spores
released
– Spores grow into
gametophyte
• Male produces sperm
• Female produces egg
– Sperm and egg make
zygote (cycle repeats)
Plant Ecology
• Mutualistic relationships
– Type of symbiosis where
both organisms benefit
– Ex: Plants (provides living
space)/Bacteria (create
nutrients)
– Ex: Plants (provide
food)/Insects (help
pollinate)
• Herbivore interactions
– Defense adaptations
– Spines, thorns, chemicals,